R290 Compressor Overheating

[Northdude]

Hey, I’m a bit stumped with this one! Ive not had many dealings with R290 but last week I was called out to a Foster Pizza Prep fridge. The compressor was down and the cabinet is on R290. I fitted a new compressor, purged the system with nitrogen, replaced the filter, put nitrogen through the capillary to make sure it’s clear of any obstruction, vacuumed and charged with R290 150g as stated on the data plate. The compressor ran and pulled down to temperature although it was running really hot, the condenser coil is clear and there are no restrictions or drop in suction pressure, the filter is just warm but the temperature of the compressor is really hot. After repeated cycles of hitting the set point etc the compressor finally goes off on internal overload due to the heat! I figured this was a faulty compressor so sent it back and replaced with a new one and I have the SAME problem! Surely 2 compressors can’t be faulty? I’m really stumped with this! The ambient in the room is about 19 degrees and condenser fan and the other intake fan are running correctly. Any advice will be great 😬

[RANGER1]

Northdude,
I think you should take some superheat readings when running & close to temperature
set point.
Can you give us suction & discharge pressures, as well as temperature set point.
Maybe nameplate incorrect if superheat way to high.

Assume compressor & oil are suitable for R290!

[Northdude]

Thanks for the reply. I’ve contacted foster and they have confirmed that the refrigerant charge is correct. I’ll call back and check the superheat and go from there. Thanks

[Northdude]

The temperature set point is 4 degrees and suction pressure on start up is 15 psi although this rises between 20 and 25 due to the heat. I don’t have discharge pressures as I’ll need to install a valve to check this.

[RANGER1]

Northdude,
I think suction pressure way to low.
You are talking 4deg C, not F are you?
40psi would be closer to the mark.
Maybe filter drier of capillary restricted, or compressor to big,
Poor airflow through evaporator, or ice build up.
Which problem one/s I don’t know.

[charlie patt]

You will probable find capillary restricted had real trouble with capiliary waxed up after comp failure in fact with a comp change on h c gas now we change capillary automatically they do run a lower suction pressure

[Northdude]

Thanks for the replies. Yes it’s 4 degrees C. I wasn’t sure with the suction pressure as it’s the first R290 system I’ve worked on so I figured it could be similar pressures to R134A. Pressure being low would make a lot of sense. The compressor is the correct size as I checked with foster. Evaporator was clean and all evaporator fans were working correctly. Firstly I better check my scales are correct and not out of calibration, then I’ll fit a larger drier and replace the capillary and try it. Thanks again ��

[RANGER1]

Thanks for the replies. Yes it’s 4 degrees C. I wasn’t sure with the suction pressure as it’s the first R290 system I’ve worked on so I figured it could be similar pressures to R134A. Pressure being low would make a lot of sense. The compressor is the correct size as I checked with foster. Evaporator was clean and all evaporator fans were working correctly. Firstly I better check my scales are correct and not out of calibration, then I’ll fit a larger drier and replace the capillary and try it. Thanks again ��

Northdude FYI if you want to achieve 4 deg C room temperature then need roughly suction to run 8-10 degrees lower than room temperature, which equals 42-46 psi.
R290 similar to R22.

[chemi-cool]

Your system is partially blocked, have it carefully checked.